Implantable power management system

ABSTRACT

The method and system for managing power supplied from a charging circuit to a power source in an implantable medical device comprises the steps of and circuitry for: measuring the current drain of the medical device; measuring the elapsed time since the last full charge of a power source of the device; calculating the actual capacity of the power source (corrected for fade) based on the variable of current drain and the variable of elapsed time; calculating the operating time based on the variable of current drain and the variable of the actual capacity of the power source; measuring the voltage of the power source; signaling the medical device when the power source voltage has reached a certain low value which requires disconnection from the power source; disconnecting, during discharging, the power source from the medical device upon the power source reaching a certain low voltage in order to prevent deep discharging of the power source and subsequent damage; precisely limiting the charging voltage to the power source in order to prevent overcharging beyond safe limits; disconnecting, during charging, the power source from the charging circuit upon the power source reaching a certain high voltage in order to prevent overcharging of the power source and subsequent damage; sensing when the electromagnetic waves being transmitted by an RF transmitter/charger induce a voltage level above a certain value at an RF receiver of the implanted power management system; reconnecting power supply inputs of the medical device to the power source upon sensing this induced high voltage level; monitoring the temperature of the power source during charging and discharging; disconnecting the charging circuitry from the power source if the temperature of the power source raises above a certain level during charging; reconnecting the charging circuitry to the power source when the temperature of the power source drops below a certain low value during charging; disconnecting the implanted medical device from the power source if the temperature of the power source raises above a certain level during discharging; and, reconnecting the medical device to the power source when the temperature of the power source drops below a certain low value during discharging.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and circuitry for safelyregulating the charge and discharge cycles of implantable grade,rechargeable power sources, utilizing inductively coupled radiofrequency energy. Patient safety and power source longevity are vastlyimproved by the method and circuitry of the system of the presentinvention. Such safety and longevity are obtained by the steps of: (1)measuring and recording, each charge/discharge cycle, to obtain thecorrected capacity of the power source in order to calculate anddisplay, upon interrogation, the remaining operating time of theimplanted device, (2) providing within the implanted medical devicecircuitry for disconnecting the power source upon reaching apre-selected low voltage in order to prevent deep-discharging the powersource below safe limits, (3) providing circuitry for using variableconstant current charge rates, (4) providing circuitry for switching toconstant voltage to top-off the power source at the completion of thecharge cycle, in order to prevent overcharging beyond safe limits, (5)providing within the implanted medical device circuitry fordisconnecting the charging circuit from the power source upon the powersource reaching a preselected high voltage level, (6) providingcircuitry for full-time RF powered operation, in case of failure of theinternal power source or for operation of the implanted medical devicerequiring extremely high power consumption (rather than being poweredfrom the internal power source of the implanted device), (7) providingcircuitry for transmitting to a remote receiver, via a telephone link,critical data that can be used by the physician and/or the devicemanufacturer to assess the performance and condition of the rechargeablepower source and the Implantable Medical Device, and (8) providingcircuitry for transmitting to the implantable medical device, via atelephone link, new operation parameter value(s).

2. Description of the Prior Art

A number of new, state-of-the-art, implantable medical devices arepowered by a rechargeable electrical power source, such as a smallvolume, large value capacitor (known as a such as a small volume, largevalue capacitor (known as a Super-capacitor), or a rechargeableelectrochemical cell. These power sources need to be periodicallyrecharged by an external Radio Frequency (RF) Transmitter via inductivecoupling in a manner known in the art.

Each type of power source has a different charge and dischargemethodology which must be faithfully followed to prevent permanentdamage to the power source. In the prior art, the charge/dischargemethodology has been factory preset via a specific hardware circuitry,suitable only for the specific power source used to power theimplantable device. Furthermore, the prior art circuitry is incapable ofproperly regulating the charge/discharge cycles of new implantable-gradepower sources, such as a Lithium-Ion cell battery.

Heretofore various battery power source charging systems have beenproposed. Examples of some of these previously proposed systems aredisclosed in the following U.S. patents:

    ______________________________________                                        U.S. Pat. No.         Patentee                                                ______________________________________                                        5,411,537             Munshi et al.                                           5,631,537             Armstrong                                               5,670,862             Lewyn                                                   5,675,235             Nagai                                                   5,764,030             Gaza                                                    5,811,959             Kejha                                                   5,818,199             Beard                                                   5,880,576             Nagai                                                   ______________________________________                                    

SUMMARY OF THE INVENTION

The present invention provides the method, software and hardware to (a)support the correct charge/discharge regimen for different types ofpower sources, (b) the capability of selecting, via software, thecorrect regimen of current and voltage limits, and (c) the capability ofnon-invasively up-grading the regimen, by down-loading, via a directtelemetry link or telephone link, new software revisions incorporatingnew improvements.

Some new state-of-the-art implantable medical devices are powered by arechargeable Super-capacitor. One limitation of a capacitive powersource is the small amount of charge that it can hold relative to anelectrochemical rechargeable cell. In the case of a Super-capacitorpowered Implantable Medical Device, when the device requires very highpower consumption, its power source must be recharged very frequently.This makes the Super-capacitor impractical as a power source for use inhigh power consumption implantable medical devices. One obvious solutionis to replace the Super-capacitor with an electrochemical cell. However,most implantable-grade, rechargeable electrochemical cells exhibit othercritical limitations when used in a hermetically sealed implantableunit. These limitations must be surmounted during the design phase ofthe charge/discharge regulating circuit for the implanted power source.

One of the power sources most suitable for use in hermetically sealed,rechargeable implantable medical devices, is the Lithium-Ion cell. Itoffers many advantages, such as relatively high energy density (highcapacity), no out-gassing during charge and discharge, high currentdelivery capabilities and relatively high output voltage. However, italso has some disadvantages, such as some loss of capacity with eachrecharge cycle (called "fade"), and the cell may be permanently damagedif allowed to be deeply discharged or overcharged. The continual loss ofcapacity (fade), requires the capability of measuring and up-linking (a)the corrected capacity value in mA-hrs, and (b) the power consumption ofthe Implanted Medical Device, in order to accurately calculate anddisplay the operating time for the Implanted Medical Device. Having thecapability of displaying the accurate operating time is extremelyhelpful to elderly patients for scheduling the next recharge session.

The power management system of the present invention provide a methodand circuitry for measuring, on a real-time basis, the current powerconsumption and elapsed time since the last full charge. This data isused by a microcontroller to calculate (a) the actual capacity(corrected for fade) of the power source, and (b) the "operating time"for the Implantable Medical Device. This operating time can be up-linkedby the Implantable Medical Device to the RF Transmitter/Charger where itcan be displayed to the patient. Thus, the patent is provided, at anytime, with an accurate prediction of the operating time as the cell'scapacity slowly fades.

If desired, the work performed by the microcontroller in the powermanagement system/module can be performed by a microcontroller of theImplantable Medical Device. In either event, the following functions areperformed:

1. Detecting whether or not an RF sensor line has switched high or low.

2. Controlling the charging rate.

3. Non-invasively changing the charge high voltage limit.

4. Switching to a constant voltage mode to top off the charge on thepower source.

5. Non-invasively changing the low voltage limit when the power sourceis disconnected during discharge.

6. Disconnecting the power source when it reaches the low voltage limit.

7. Reconnecting the power source upon sensing the transmission of RFenergy.

8. Disconnecting the power source upon sensing a high temperature.

9. Reconnecting the power source when the temperature drops to a normallevel.

10. Measuring the power consumption of the circuitry for the ImplantableMedical Device.

11. Measuring the elapsed time since the last full charge.

12. Tracking the actual capacity of the power source.

13. Calculating the operating time left for the Implantable MedicalDevice.

It is an aspect or objective of the present invention to provide: (1) amethod and circuitry for measuring the current drain of the ImplantableMedical Device, (2) a method and circuitry for measuring the elapsedtime since the last full charge, (3) a method for calculating the actualcapacity of the power source (corrected for fade) based on the variableof current drain and the variable of elapsed time, (4) a method forcalculating the operating time based on the variable of current drainand the variable of the actual capacity of the power source, (5) amethod and circuitry for measuring the voltage of the power source, (6)a method and circuitry to signal the Implantable Medical Device when thepower source voltage has reached a certain low value which requiresdisconnection from the power source, (7) a method and circuitry fordisconnecting, during discharging, the power source from the ImplantedMedical Device upon the power source reaching a certain low voltage inorder to prevent deep discharging of the power source and subsequentdamage, (8) circuitry for precisely limiting the charging voltage to thepower source in order to prevent overcharging beyond safe limits, (9) amethod and circuitry for disconnecting, during charging, the powersource from the charging circuit upon the power source reaching acertain high voltage in order to prevent overcharging of the powersource and subsequent damage, (10) circuitry for sensing when theelectromagnetic waves being transmitted by the RF Transmitter/Chargerinduce a voltage level above a certain value at the RF Receiver of theImplanted Power Management System, (11) circuitry for reconnecting thepower supply inputs of the Implanted Medical Device to the power sourceupon sensing this induced high voltage level, (12) a method andcircuitry for monitoring the temperature of the power source duringcharging and discharging, (13) circuitry for disconnecting the chargingcircuitry from the power source if the temperature of the power sourceraises above a certain level during charging, (14) circuitry forreconnecting the charging circuitry to the power source when thetemperature of the power source drops below a certain low value duringcharging, (15) circuitry for disconnecting the implanted Medical Devicefrom the power source if the temperature of the power source raisesabove a certain level during discharging, (16) circuitry forreconnecting the Implantable Medical Device to the power source when thetemperature of the power source drops below a certain low value duringdischarging, (17) a method and circuitry for transmitting to a remotedevice, via a telephone link, data that can be used by the physicianand/or the device manufacturer to assess the performance and conditionof the rechargeable power source and the Implantable Medical Device, and(18) a method and circuitry for transmitting via a telephone link to,and setting in, the Implantable Medical Device, new operationalparameter value(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block plan view of one embodiment of the power managementsystem of the present invention and shows a charge monitor, an RFtransmitter, an Implanted Medical Device (Neural Stimulator) withexterior RF pick up coil and a telephone link.

FIG. 2 is block plan view of another embodiment of the power managementsystem of the present invention, similar to the view shown in FIG. 1,and shows a charge monitor, an RF transmitter, an Implanted MedicalDevice (Neural Stimulator) without an exterior RF pick up coil and atelephone link.

FIG. 3 is a block plan view of a physician programmer and a telephonelink for communicating with the power management system shown in FIG. 1or in FIG. 2.

FIG. 4 is a block electrical schematic circuit diagram of the powermanagement module located inside the Implanted Medical Device.

FIG. 5 is a block schematic circuit diagram for a voltage regulatorhaving an output whose voltage value is adjusted by a bus.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 illustrates the power management system 1 of the presentinvention. The system 1 utilizes an implanted RF receiving antenna 2located outside of an Implantable Medical Device 4. This RF receivingantenna 2 is used for capturing RF electrical energy 5 being transmittedby an RF Transmitting Antenna 6 located outside the human body tissue 7.The Implanted Medical Device 4 is typically enclosed in a hermetictitanium housing 4A in order to prevent intrusion of the body fluidswhich would permanently damage its sensitive electronic circuitry 8.This titanium housing 4A significantly attenuate and reduces the RFenergy that can be coupled through the titanium enclosure 4A. Therefore,in FIG. 1, the RF receiving antenna 2 is placed outside of the ImplantedMedical Device 4 but inside the human body, using insulated wires in acable 9 to bring the coupled RF energy to the Implanted Medical Device 4in order to recharge its power source 10.

FIG. 2 shows an embodiment of the Power Management System 1 without theexternal Rf antenna 2 and, instead, shows an RF receiving antenna 3which is located inside of the Implantable Medical Device 4 forcapturing the RF electrical energy 5 being transmitted by the RFtransmitting antenna 6 located outside the human body. In thisembodiment, a more compact Implantable Medical Device 4 is provided byplacing the RF receiving antenna 3 inside the hermetic titaniumenclosure 4A of the Implanted Medical Device 4. This compactness isachieved at the expense of reducing the amount of RF energy that can becoupled into the Implanted Medical Device 4. This requires transmittingsubstantially higher levels of RF energy, significantly decreasing thelongevity of the battery powering an RF Transmitter Unit 13.

FIG. 4 is a block schematic circuit diagram of the circuitry 8 for aPower Management System Module 11 located inside the Implanted MedicalDevice 4. The function of the Power Management Module 11 is to supervisethe charging and discharging operations of the rechargeable power source10 powering the Implantable medical Device 4, in order to improve thesafety, efficacy and reliability of the rechargeable power source 10.This Power Management Module 11 incorporates distinctive circuitry andmethods for operating same to: (a) sense when the RF energy coupled intothe RF Receiver exceeds the minimum level for safe operation of theImplantable Medical Device, (b) adjust the rate of charge to the powersource 10, (c) precisely regulate the voltage used to charge the powersource, (d) non-invasively adjust the level of this charge voltage, (e)allow unidirectional current flow from the voltage regulator to thepower source, (f) provide a low impedance path from the power source tothe VDD connection supplying the operating power to a Power ManagementModule Controller 100 when the RF signal is not sensed, (g) sense thetemperature of the power source, (h) disconnect the V-supply to theImplantable Medical Device 4 upon sensing a battery temperature whichexceeds a safe value during discharging, (i) reconnect the V+ supply tothe Implantable Medical Device upon the battery temperature dropping toa safe value during discharging, (j) disconnect a charging circuit 60Afrom the power source 10 upon sensing a battery temperature exceeding asafe value during charging, (k) reconnect the charging circuit 60A tothe power source upon the battery temperature dropping to a safe valueduring charging, (l) disconnecting the charging circuit 60A from thepower source upon sensing a "full" voltage level at the power source 10,(m) non-invasively adjust the value of this "full" voltage, and (n)reconnect the charging circuit 60A to the power source when the RFenergy coupled into the RF Receiver exceeds the minimum level for safeoperation of the Implantable Medical Device 4.

Referring again to FIG. 1, there is illustrated therein the maincomponents of the Power Management System 1 used for maximum RFefficiency, where the RF receiving antenna 2 is placed outside thehermetic titanium enclosure 4A of the Implanted Medical Device 4. ThePower Management System 1 is used to safely manage the charging anddischarging of the power source 10 powering the Implantable MedicalDevice 4.

On the right half of FIG.1, the main components of the Power ManagementSystem comprise: (a) Charge Monitor 20 which is used to display the"remaining operating time" and "corrected capacity" of the power source10 powering the Implantable Medical Device 4, (b) an RF Transmitter Unit13 used to generate the RF signal to be transmitted by antenna 6, (c)plug 18 which is used to connect the RF Transmitter Unit 13 to antenna6, (d) RF Receiving Antenna 2 which is used to pick-up the RF energy 5transmitted by antenna 6, (e) cable 9 which are used to bring inside theImplantable Medical Device 4 the induced RF energy, (f) Power ManagementModule 11 which is used to safely manage the charge/discharge cycles ofthe power source 10 powering the Implantable Medical Device 4 and tocollect performance data, and (g) rechargeable power source 10 used topower the Implantable Medical Device.

RF Transmitter Unit 13 can be used as a stand-alone device when theImplantable Medical Device 4 must be powered full-time via RF coupledenergy. When used for full-time RF power, a switch 14 must be switchedto the "IRF" position. When the Implantable Medical Device 4 is to bepowered by its own rechargeable power source 10, RF Transmitter Unit 13is used to generate the RF energy used to recharge the power source 10.In this case, the switch 14 of RF Transmitter Unit 13 must be switchedto the, "self" position and a plug 17 of RF Transmitter Unit 13 must beplugged into a jack 29 of the Charge Monitor 20. An A/C Transformer 45can be used to power the Charge Monitor 20, or alternatively the ChargeMonitor 20 can be powered by its own internal battery.

Referring to the Charge Monitor 20, a liquid crystal display 21 is usedto display critical data, such as the "number of charge/dischargecycles" of the power source 10. Push button 22 is used to scroll thedisplay 21 to the next data, such as the "corrected capacity" of thepower source 10. The push button 22 "oper. time" is used to display theremaining operating time of the Implantable Medical Device 4 based oncurrent power consumption and the present capacity of the power source10. Push button 24 is used by the patient to return the ImplantableMedical Device 4 to safe "default" parameter value(s) when newlyprogrammed values via the Phone Link do not work correctly for thepatient. Push button 25 is used to abort a charge cycle to the powersource 10. Push button 26 is used to initiate a charge cycle for thepower source 10. Push button 27 is used to power-up or power-down theCharge Monitor 20.

On the left side of FIG. 1, the remaining system components comprise:Phone Link coupler 33 which is used to convert digitally coded signalsinto audible distinctive "tones". These converted "tones" are sent to astandard telephone 44 via jack 30, plug 42 and cable 43. Note that datacommunications between Phone Link coupler 33, telephone 44 and thepublic telephone system is made via a cable 37, plug 38 and jack 39 oftelephone wall plug 40. Also, note that data communications betweenPhone Link 33 and Charge Monitor 20 is made via a cable 32, plug 31 andjack 28.

Referring now to FIG. 2, there is illustrated therein the maincomponents of the Power Management System 1 used for a maximumvolumetric efficiency, where the RF Receiving Antenna 3 is placed insidethe hermetic titanium enclosure 4A of the Implanted Medical Device 4,rather than outside. Other than this simple difference, the PowerManagement System shown in FIG. 2 is identical to that of FIG. 1.

Referring now to FIG. 3, the other side of the telephone link circuit iscompleted by using a "Physician Programmer" 50 which is connected, viaanother Phone Link coupler 51, to another telephone 52 having aconnection established, via telephone 44 of FIG. 1, to the ChargeMonitor 20 of FIG. 1.

By pressing push button 53, the physician or the manufacturer of theImplantable Medical Device 4 can retrieve data representing thecondition of the rechargeable power source 10 and of the ImplantableMedical Device 4.

By pressing push button 54, the physician can program new operatingparameters values into the Implantable Medical Device 4. It should beobvious that the circuitry within the Phone Link 51 can be incorporatedinto the Physician Programmer 50 to accomplish the same goal.

Referring now to FIG. 4, there is illustrated therein a block schematiccircuit diagram of the circuitry 8 for the Power Management Module 11used to safely manage the charge and discharge cycles of the powersource 10 powering the circuitry 8 of the Implantable Medical DeviceCircuit 4.

The following is a detailed narrative of the operation of each circuitcomponent shown in FIG. 4.

Coupling RF Energy into the Implantable Medical Device.

On the top-left side of FIG. 4, there is shown a RF Receiver 55comprising the RF Receiving Antenna 2 used to pick-up the transmitted RFenergy 5, capacitor 56 used for tuning the antenna 2 to the specific RFfrequency to be transmitted, back-to-back Zener diodes 57 which are usedto limit the maximum voltage that can develop across the antenna 2 inorder to protect the charging circuit 60A comprising a Voltage Regulator61 from over-voltage, a bridge 58 used for rectifying the RF energy intoa DC voltage, and a capacitor 59 used for smoothing the output 60 of thebridge 58 to a steady DC voltage.

Operation of the RF Sensor.

On the top-middle of FIG. 4, there is shown an RF Sensor 67 which isused to sense when the voltage at line 60 has risen above a presetvoltage indicating that the level of RF energy is sufficiently high toprovide the current required to charge power source 10. When the voltageat line 60 reaches the reverse breakdown voltage of a Zener diode 68connected as shown, sufficient voltage will develop at resistor 69 toturn on transistor 70, causing line 72 to switch low.

A microcontroller 100 detects this signal change and responds byswitching line 85 high which turns on transistor 87 and connects thepower source 10 to the common ground.

Controlling the Charge Rate Using a Closed-Loop Method.

The Charge Rate Control 73 is used, under the supervision ofmicrocontroller 100, to regulate the constant current value used tocharge the power source 10. Microcontroller 100 applies a square wave atline 74 which is directed to the cathode of diode 75. During eachnegative half-cycle, diode 75 becomes forward biased and some charge isinjected into capacitor 77 through resistor 76. However, during eachpositive half-cycle a smaller charge bleeds off from capacitor 77through larger resistor 78 since diode 75 is reverse biased. The resultis that a specific residual voltage develops at capacitor 77 due to thesquare wave at line 74. The specific voltage value depends on thefrequency and duty cycle of the square wave and the resistance ratiobetween resistors 76 and 78. This residual voltage at line 82 drivestransistor 79 in a constant current mode.

As transistor 79 sources current into the power source 10, a voltagewill develop across resistor 81. This voltage is amplified by amplifier83 and sampled by channel 4 of the A/D converter in micro-controller100. Therefore, a closed-loop charging method is created where thecharge rate is precisely regulated within a wide range bymicrocontroller 100. The charge rate is regulated by varying thefrequency and/or duty cycle at line 74 until the desired current ismeasured by the A/D in the microcontroller 100. This closed-loop methodpermits adjusting the charging rate to the specific value recommended byeach manufacturer of the power source 10, thus providing a universalcharging method suitable for different types of power sources 10. Thisclosed-loop method, also permits an initial fast charge rate in order toquickly reach the minimum operating voltage of the power source 10 ofthe Implantable Medical Device 4 to enable therapy, and then switch to alower rate which is more benign to the life of the power source 10.

Also, since typically the Implantable Medical Device 4 incorporates atelemetry circuit to communicate with an external device, such as thePhysician Programmer 50 of FIG. 3, the charge rate can be non-invasivelychanged after implant by down-loading new values via the PhysicianProgrammer 50.

Switching to a Constant Voltage Mode to Top-Off the Cell.

Once the power source 10 has reached a voltage close to its maximumrated voltage, charging is switched from constant current to constantvoltage to preclude exceeding the maxim voltage recommended by themanufacturer. As an example, for a Lithium-Ion cell, the maximum valueis typically 4.1 volts. For this example, microcontroller 100 will setthe voltage regulator 61 to output 4.1 volts. Once the power source 10has reached approximately 3.9 volts while charging at constant current,microcontroller 100 will fix line 74 high and line 64 low. This willturn off transistor 79 (constant current) and turn on transistor 65(constant voltage), limiting the power source 10 to 4.1 volts when fullycharged.

Disconnecting the Power Source to Avoid Deep Discharging.

Microcontroller 100 incorporates a digital to analog converter having atleast four channels: A/D1, A/D2, A/D3 and A/D4. A/D1 is used to monitorthe voltage at the power source 10. During discharging of the powersource 10, when the voltage at line 95 reaches a preset low value,microcontroller 100 will initiate the following power-down protocol:

1. Microcontroller 100 will signal the circuitry 8 of the ImplantableMedical Device 4 to perform the necessary housekeeping chores to preparefor a power shut-down.

2. The microcontroller 100 will "float" the line 85 if no RF energy isbeing sensed by RF Sensor 67 (line 72 is high). This will turn offtransistor 87, effectively disconnecting the power source 10 from thecommon ground. This is done to preclude damaging the power source 10 ifallowed to be deeply discharged. Such will be the case for a Lithium-Ioncell. Note that the power is disconnected from the Power ManagementModule 11 and the circuitry 8 of the Implantable Medical Device 4, thusremoving all loads from the power source 10.

Reconnecting the Power Source Upon Sensing the Transmission of RFEnergy.

As explained previously, RF Sensor 67 is used to sense when the level ofRF energy 5 is sufficiently high to provide the current required tocharge the power source 10. When adequate proximity and alignment isachieved between the charging antenna 6 and receiving antenna 2 (or 3)of FIG. 1 (or FIG. 2), line 72 will switch low, and in response,microcontroller 100 will switch line 85 high, reconnecting power source10 to the common ground, and getting it ready for charging.

Disconnecting the Power Source Upon Sensing a High Temperature at thePower Source During Discharge.

On the bottom-right of FIG. 4, there is shown Temperature Sensor 98whose output line 99 is connected to an A/D Converter channel A/D3. Whenthe temperature of power source 10 is nearing an unsafe value which is asoftware loaded variable, microcontroller 100 will "float" line 104,switching off transistor 103. This effectively disconnects power source10 from the circuitry 8 Implantable Medical Device 4. Note that thepower source 10 will continue to power the microcontroller 100 (throughthe line 80, transistors 65 and the VDD supply) in order for themicrocontroller 100 to sense when the temperature drops to a safe levelby monitoring line 99.

Reconnecting the Power Source When the Temperature Drops to a SafeLevel.

When the temperature of the power source 10 drops to a safe level,microcontroller 100 will switch line 104 high which will turn ontransistor 103, effectively reconnecting the power source 10 to thecircuitry 8 of the Implantable Medical Device 4.

Measuring the Power Consumption of the Implantable Medical Device.

On the center right of FIG. 4, there is shown the Current Measurementcircuit 88 which comprises transistor 94 and its control line 93,voltage-dropping resistors 90 and 91, averaging capacitor 92, amplifier89, and output line 96. As current is sourced into to the circuitry 8 ofthe Implantable Medical Device 4, a voltage drop will develop across theresistance path formed by resistors 90 and 91. This voltage drop isamplified by Amplifier 89 and directed to the A/D Converter channel A/D2in microcontroller 100. Since Amplifier 89 has a gain of 100, ifresistors 90 and 91 are assigned values of 1 and 9 Ohms, respectively,the voltage at line 96 will be 1 volt for a current drain of 10 mA(transistor 94 is switched on, shunting resistor 91). For lower currentdrains, microcontroller 100 will turn off transistor 94 to increase thevoltage-dropping resistance to 10 Ohms. Therefore, high and low currentdrain scales are achieved. The circuitry 8 of the Implantable MedicalDevice 4 will communicate to microcontroller 100 the scale to be useddepending on the parameter values presently being used by theImplantable Medical Device 4.

Measuring the Elapsed Time Since the Full Charge.

On the top center of FIG. 4 there is shown microcontroller 100 which isalso used to count the elapsed time since the last full charge. When theRF Transmitting Antenna 6 of FIG. 1 is removed from the RF Receivingantenna 2 (or 3 in FIG. 2), RF Sensor 67 will sense this event causingline 72 to switch high.

Microcontroller 100 will sense the rise of line 72 and will startcounting the elapsed time in days, hours and minutes, using a typicalsoftware timing loop known in the art.

Tracking the Capacity of the Power Source as the Charge/Discharge Cyclesare Used Up.

The measured elapsed time from full charge to a full discharge inconjunction with the measured current drain, is used by microcontroller100 to calculate the actual capacity of power source 10. Therefore, thecapacity value is corrected for the fading effects caused by eachcharge/discharge cycle. Note: A full discharge refers to a power sourcedischarged only to the lowest voltage recommended by the manufacturer ofpower source 10. In the case of a Lithium-Ion cell this low voltage istypically 3.0 volts.

Calculating the Operating Time of the Implantable Medical Device.

The operating time from any point in the discharge curve of power source10 to a full discharge, can be calculated by microcontroller 100 whichmeasures (a) the average mA being consumed by the Implantable MedicalDevice 8, (b) the elapsed time since the last charge, and (b) the actualcapacity of power source 10. The remaining operating time is calculatedby: (1) multiplying the mA being consumed by the elapsed time in hoursto arrive at the "consumed" capacity, (2) subtracting this "consumed"capacity from the "actual" (total) capacity to arrive at the "remaining"capacity, and (3) dividing the mA being consumed into the "remaining"capacity value of mA/hrs to arrive at the hours of operating time anddividing the answer by 24 to convert hours to days. Note that the powerconsumption of the Power Management Module 11 is insignificant (lessthan 3 uA) and therefore can be ignored in the calculation.

Referring now to FIG. 5, there is illustrated therein a block schematiccircuit diagram of the Voltage Regulator 61 with output 62 whose voltagevalue is adjusted by a bus 66. Microcontroller 100 controls the state ofbus lines 106, 107, 108 and 109. These lines in turn control the stateof transistors 110, 111, 112 and 113. These transistors are used toselect the total value of resistance in the voltage sense loop for thevoltage regulator 61. By adjusting the ratio of resistor 114 to thecombined resistance of resistors 106, 107, 108 and 109, the outputvoltage of the voltage regulator 61 can be adjusted anywhere between 2.5to 5.5 volts. This range covers the voltage required by most implantablegrade, rechargeable power sources, including Lithium-Ion cell, VanadiumOxide cell and a Super-capacitor.

From the foregoing description, it will be apparent that the method andsystem for power management of the present invention have a number ofadvantages, some of which have described above and others which areinherent in the invention. Also, it will be understood thatmodifications can be made to the method and system for power managementof the present invention without departing from the teachings of thepresent invention. Accordingly, the scope of the invention is only to belimited as necessitated by the accompanying claims.

What is claimed is:
 1. A method for managing the power supplied to apower source of an implantable medical device comprising the stepsof:(a) providing charging circuitry for a power source in an implantablemedical device; (b) selecting from software in the charging circuitrythe correct charge/discharge regimen for the specific power source inthe implantable device; (c) charging the power supply with the correctregimen of current and voltage limits for the specific power; and, (d)non-invasively up-grading the regimen for charging the power source, bydown-loading, via a direct telemetry link or telephone link, newsoftware revisions to the regimen.
 2. A system for managing the powersupplied to a power source of an implantable medical devicecomprising:charging circuitry for a power source in an implantablemedical device; software in the charging circuitry for the correctcharge/discharge regimen for the specific power source in theimplantable device; charging the power supply with the correct regimenof current and voltage limits for the specific power source; and,circuitry for non-invasively up-grading the regimen for charging thepower source, including circuitry for down-loading, via a directtelemetry link or telephone link, new software revisions to the regimen.